Fuel injection valve

ABSTRACT

A fuel injector ( 1 ) for the direct injection of fuel into a combustion chamber of an internal combustion engine includes a piezoelectric or magnetostrictive actuator ( 3 ) and a valve-closure member ( 11 ) able to be actuated by the actuator ( 3 ), the valve-closure member ( 11 ) cooperating with a valve-seat surface ( 12 ) to form a sealing seat, a compensation gap ( 9 ) being present in an actuation path between the actuator ( 3 ) and the valve-closure member ( 11 ). A measuring element ( 13 ) is provided in the actuator ( 3 ) and/or in the actuation path, the measuring element ( 13 ) measuring the forces exerted by the actuator ( 3 ) the valve-closure member ( 11 ) and the actuator ( 3 ) being regulated in such a way that the compensation gap ( 9 ) is being held closed.

BACKGROUND INFORMATION

[0001] The present invention is directed to a fuel injector of the type set forth in the main claim.

[0002] For instance from DE 198 49 203 A1, a fuel injector for fuel-injection systems of internal combustion engines is known. It includes a valve-closure member cooperating with a valve-seat body to form a sealing seat, and a piezoelectric actuator for actuating the valve-closure member. The piezoelectric actuator has piezo-layers and one or a plurality of temperature-compensation layers. The temperature-compensation layers have a thermal expansion coefficient whose sign is the opposite of that of the thermal expansion coefficient of the piezo-layers.

[0003] Furthermore, from DE 199 18 976 A1, a fuel injector for fuel-injection systems of internal combustion engines is known, which includes a first piezoelectric or magnetostrictive actuator, a valve-closure member, which is actuable by the first actuator by means of a valve needle and cooperates with a valve-seat surface to form a sealing seat, and has a second piezoelectric or magnetostrictive actuator, which acts upon the valve needle counter to the first actuator. The actuators are arranged one after another in the longitudinal direction of the fuel injector and are interconnected by a bearing element, which is permanently supported in the fuel injector.

[0004] Disadvantageous in the fuel injector known from DE 198 49 203 A1 is that the temperature compensation is implemented by special layers within the actuator, the material of these temperature-compensating layers exhibiting thermal expansions acting in opposite directions. This causes problems, in particular during rapid dynamic operations, since the different materials react differently, due to the dissimilar thermal expansion coefficients. Furthermore, a special actuator with temperature-compensation layers must be developed.

[0005] A disadvantage of the fuel injector known from DE 199 18 976 A1 is the large overall length that the axially offset arrangement of the actuators necessitates. Also, this large overall length goes hand in hand with a widening of the fuel injector, which the support of the bearing plate calls for.

SUMMARY OF THE INVENTION

[0006] In contrast, the fuel injector according to the present invention, having the characterizing features of the main claim, has the advantage over the related art that conventional stack actuators, or actuators having a plurality of separated regions with compensation elements, are able to be controlled by a measuring and regulating device, in such a way that a play compensation for the temperature-related linear deformations of the actuator may be achieved in a simple and inexpensive manner, without the use of expensive INVAR materials.

[0007] In this context, it is furthermore advantageous that the separate controlling of the opening actuator and the compensation actuator may be implemented at different speeds, so that the dynamic performance of the fuel injector is not adversely affected, yet the temperature compensation may occur slowly.

[0008] Advantageous further developments of the fuel injector specified in the main claim are rendered possible by the measures elucidated in the dependent claims.

[0009] In an advantageous manner, the measuring element may be positioned anywhere on the actuator in the flux of force in front of the compensation gap. A prestressing against the measuring element may be achieved by the joint clamping of the measuring element inside the actuator cartridge.

[0010] Furthermore, it is advantageous that the measuring element may also be located outside the actuator, for instance may be integrated in the actuating element.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Exemplary embodiments of the present invention are shown in simplified form in the drawing and are elucidated in greater detail in the following description.

[0012] The figures show:

[0013]FIG. 1A a highly schematized, sectioned representation of a first exemplary embodiment of a fuel injector configured according to the present invention;

[0014]FIG. 1B a highly schematized, sectioned representation of a second exemplary embodiment of a fuel injector configured according to the present invention;

[0015]FIG. 2A a schematic view of a stack actuator of the fuel injector configured according to the present invention;

[0016]FIG. 2B a schematic view of an actuator of the fuel injector configured according to the present invention, the actuator having separate control regions;

[0017]FIG. 3A a schematic representation of the time characteristic of the forces acting on the actuator, without a compensation actuator; and

[0018]FIG. 3B a schematic representation of the time characteristic of the forces acting on the actuator, with a compensation actuator.

DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

[0019] In a highly schematized sectioned view, FIG. 1A shows a longitudinal section through the essential components of a fuel injector 1 configured according to the present invention. Fuel injector 1 is embodied as a fuel injector for mixture-compressing internal combustion engines having external ignition. It is especially suited for the direct injection of fuel into a combustion chamber of an internal combustion engine.

[0020] Fuel injector 1 encompasses a housing 2 in which a piezoelectric actuator 3 is arranged. Piezoelectric actuator 3 may be made up, for instance, of a plurality of interconnected piezoelectric layers 14. Actuator 3 is encapsulated in an actuator cartridge 4 and prestressed by a compression spring 5 clamped between actuator 3 and actuator cartridge 4. The encapsulation of actuator 3 is required to protect actuator 3 from chemical damage by the fuel. On the other hand, actuator 3, already preassembled in actuator cartridge 4, is easier to install and, in addition, is protected from damage by mechanical stresses during the installation.

[0021] By way of a downstream-side end 6, actuator 3 is braced against an actuating member 7 having the form of a piston.

[0022] On the downstream side of actuating member 7 is a valve needle 8, which is set apart from actuating member 7 by a compensation gap 9. Valve needle 8 has on its downstream-side end 10 a valve-closure member 11, which forms a sealing seat together with a valve-seat surface 12 formed on housing 2 of fuel injector 1. The exemplary embodiment shows an outwardly opening fuel injector 1.

[0023] On the downstream side of compensation gap 9, valve needle 8 is guided by two guide elements 18 and 20. To return valve needle 8 when actuator 3 is non-energized, a restoring spring 19 is provided, which is clamped between valve-needle guide 20 and a disk 21 connected to valve needle 8 by force-locking.

[0024] According to the present invention, fuel injector 1 has a measuring element 13, which is located at an arbitrary location in an actuating path, which encompasses actuating member 7 and valve needle 8, between actuator 3 and valve-closure member 11. In the present first exemplary embodiment, measuring element 13 is disposed between an end face 14 of actuator cartridge 4 and an inflow-side end 15 of actuator 3. However, as shown in FIG. 1B, measuring element 13 may also be situated between the downstream-side end 6 of actuator 3 and actuating member 7, so that compression spring 5 is braced against measuring element 13.

[0025] As an alternative, measuring element 13 may also be integrated in actuating member 7, as is shown in FIG. 1B as well. Furthermore, actuator 3 may be encapsulated in different ways and prestressed, too, which allows measuring element 13 to be positioned at different points in the flux of force. It must merely be ensured that measuring element 13 is positioned on the inflow side of compensation gap 9.

[0026] In order to control the width of compensation gap 9 formed between actuating member 7 and valve needle 8 in such a way that undesired opening phases of fuel injector 1 are prevented, these opening phases being caused by linear deformations of actuator 3 due to thermal effects, and in order to achieve a constant opening lift of valve needle 8, the present invention provides for measuring element 13. Measuring element 13 measures the forces exerted by actuator 3. By a control loop (not shown further), the actuator voltage and the voltage of a compensation actuator 16 may be regulated in such a way that a reliable play compensation is attained, without the dynamic properties of actuator 3 being affected in a detrimental manner.

[0027]FIGS. 2A and 2B show two exemplary embodiments of possible actuators 3. FIG. 2A shows a stack actuator 3, which is made up of individual piezoelectric layers 14. One or a plurality of layers 14 may be designed as compensation layers, or be configured as compensation actuator 16 in their entirety and integrated in stack actuator 3. Measuring element 13 is arranged at an arbitrary location inside stack actuator 3. A measuring voltage U_(M) is tapped off on one side on actuator 3, so that the pressure force may be measured. Actuator voltage U_(A) is applied on the other side of measuring element 13.

[0028] As shown in FIG. 2B, compensation actuator 16 may also be configured in the form of a separate compensation actuator 16, for instance. In this case, actuator 3, in its entirety, is made up of an opening actuator 17, a compensation actuator 16 and measuring element 13. Each part is separately controllable. Lines that are at the same potential, such as the ground lines, may also be brought together to simplify matters.

[0029]FIGS. 3A and 3B illustrate force F, which is exerted by actuator 3 and measured by measuring element 13.

[0030] In FIG. 3A, the sole force F_(A) of opening actuator 17, which is formed either from the totality of layers 14 of stack actuator 3 acting in the opening direction according to FIG. 2A, or by one-piece compensation actuator 16 according to FIG. 2B, is represented as a function of time t. Due to the high dynamics of piezoelectric actuators 3, a nearly rectangular force characteristic is representable, which extends over opening time t_(i). A play compensation is not possible here.

[0031]FIG. 3B shows the combined effect of opening actuator 17 and compensation actuator 16.

[0032] Between two injection cycles, a small excitation voltage is supplied to compensation actuator 16 by which compensation actuator 16 expands to the point where compensation gap 9 is closed. Measuring element 13 detects closed compensation gap 9 by an increase in the pressure force acting on measuring element 13. The play compensation is ended at a point at which the pressure force is not yet sufficient to actuate valve needle 8. To compensate for the temperature-related changes in length, the play compensation is implemented more slowly than the opening operation of fuel injector 1.

[0033] If fuel injector 1 is activated by actuating opening actuator 17, compensation gap 9 is closed and the movement of opening actuator 17 is immediately transmitted to valve needle 8 via actuating element 7. The excitation voltage for compensation actuator 16 may be maintained during the open phase of fuel injector 1 or it may be switched off in order to damp valve needle 8.

[0034] When fuel injector 1 is closed, both excitation voltages are switched off, so that all actuator regions return to their neutral state for the next injection cycle.

[0035] Alternatively, compensation actuator 16 may also be kept under voltage over the entire injection cycle. The play compensation may then be carried out continually. A charge loss of the compensation actuator may be compensated for by recharging. During the injection intervals, measuring element 13 checks that the allowed maximum force of the compensation actuator is not exceeded, in order to prevent an undesired opening of fuel injector 1. Compensation actuator 16 may be discharged continually or in a step-by-step manner, or may be separated from the voltage source completely. In the process, corresponding algorithms of the control loop take into account the temperature of fuel injector 1, temperature changes, the load state of the internal combustion engine as well as learned values from preceding injection cycles.

[0036] The present invention is not limited to the exemplary embodiments shown and applicable, for instance, also to magnetostrictive actuators 3, for arbitrary designs of measuring elements 13 and various designs of fuel injectors 1. 

What is claimed is:
 1. A fuel injector (1) for the direct injection of fuel into a combustion chamber of an internal combustion engine, comprising a piezoelectric or magnetostrictive actuator (3) and a valve-closure member (11) actuatable by the actuator (3), the valve-closure member (11) cooperating with a valve-seat surface (12) to form a sealing seat, a compensation gap (9) being present in an actuation path between the actuator (3) and the valve-closure member (11), wherein a measuring element (13) is provided in the actuator (3) and/or in the actuation path, the measuring element (13) measuring the forces exerted by the actuator (3) on the valve-closure member (11) and the actuator (3) is regulated in such a way that the compensation gap (9) is held closed.
 2. The fuel injector as recited in claim 1, wherein the actuation path encompasses an actuating member (7), which is in operative connection with the actuator (3), and a valve needle (8), which is in operative connection with the valve-closure member (11).
 3. The fuel injector as recited in claim 2, wherein the compensation gap (9) is formed between the actuating member (7) and the valve needle (8).
 4. The fuel injector as recited in one of claims 1 through 3, wherein the actuator (3) has an opening actuator (17) and a compensation actuator (16).
 5. The fuel injector as recited in one of claims 1 through 4, wherein the actuator (3) is encapsulated in an actuator cartridge (4).
 6. The fuel injector as recited in claim 5, wherein a compression spring (5) keeps the actuator (3) prestressed in the actuator cartridge (4).
 7. The fuel injector as recited in one of claims 1 through 6, wherein the measuring element (13) is arranged inside the actuator cartridge (4).
 8. The fuel injector as recited in one of claims 1 through 6, wherein the measuring element (13) is arranged at any location outside the actuator cartridge (4) in the flux of force.
 9. The fuel injector as recited in claim 2 or 3, wherein the measuring element (13) is integrated in the actuating member (7).
 10. The fuel injector as recited in claim 4, wherein the opening actuator (17) and the compensation actuator (16) are made up of individual piezoelectric or magnetostrictive layers (14) and form a joint stack actuator.
 11. The fuel injector as recited in claim 10, wherein the measuring element (13) encompasses one or a plurality of layers (14) of the stack actuator.
 12. The fuel injector as recited in one of the claims 4, 10 or 11, wherein the compensation actuator (16) and the opening actuator (17) form separate regions of the piezoelectric or magnetostrictive actuator (3). 